David Krofcheck

on behalf of the CMS Collaboration

IAS-CERN Workshop, Singapore, March 26th

Heavy Ion Collision Measurements at the LHC Using the CMS Detector

So, what happens at the LHC besides Higgs hunting?

p, K, p, n, f, L, D, X, W, d

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The CMS Detector - Overall picture

Pixel and Silicon-Strip Tracker

Excellent momentum resolution

Large acceptance || < 2.5

3.8 T Solenoid

Hermetic calorimeter coverage

ECAL + HCAL || < 3.0

Forward HCAL 3.0 || < 5.0

DAQ+Trigger: Dedicated triggers for Jets, Photons, Muon, high pT charged particles, etc.

Muon Detectors

|| < 2.5

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Beam Scintillators (NZ)

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• Basic nuclear physics jargon as needed

• Probing the sQGP with the CMS …highlights, too much to discuss!

• Dijets – energy balance

• γ – jet energy loss

• Electroweak probes (Z0 ,W±),

• Quarkonia suppression

• Nuclear Modification Factors (RAA)

• Particle correlations

“flow”, dihadrons

• Basic Summary

4T

The CMS Detector - single particle detection

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The CMS Detector - better than a cartoon

• Measure the overlap of two ions or number of

“participating” or “colliding” nucleons by measuring energy

in forward calorimeters

• Energy in calorimeters is ~ to the number of participating

nucleons in the overlap region (Glauber Model)

• Rate of high pT processes is ~ to the number of colliding

pairs of quarks and gluons

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What Pixel detectors and Forward calorimeters “see”

“central” “central” “peripheral” “peripheral”

Jet production in pp collisions

jet-jet correlation in QCD “vacuum”

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Jet production in PbPb collisions

jet-jet correlation in QCD “medium”

γ – jet correlation to probe the medium?

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E-ΔΕ1

E-ΔΕ2

Dijet imbalance in PbPb collisions Δφ

Phys. Rev. C 84, 024906 (2011)

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Selecting jets in PbPb collisions

“peripheral” “central”

Phys. Rev. C 84, 024906 (2011)

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Dijets in PbPb - asymmetry in central collisions

PLB 712 (2012) 176

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Observed momentum imbalance in γ – jet correlation

Wang&Zhu arXiv:1302.5874

Linar Boltzman Transport

∙elastic parton scattering

∙induced gluon emission

PLB 718 (2013) 773

• Significant deviation of ⟨xJ⟩ in PbPb compared to PYTHIA + HYDJET

Mean xJ

Observed deviation between γ – jet from PbPb collisions

CMS

Wang & Zhu arXiv:1302.5874

PLB 718 (2013) 773

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Observed deviation between γ – jet from PbPb collisions

Wang & Zhu arXiv:1302.5874

PLB 718 (2013) 773

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PRL 106 (2011) 212301 PLB 715 (2012) 66 D. Krofcheck IAS-CERN Workshop, Singapore 17

Electroweak bosons passing through sQGP

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PLB 710 (2012) 256

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EPJC 72 (2012)1945

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Heavy Mesons as sQGP Thermometers

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Upsilon ( ϒ ) excited state sequential “melting”

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Dimuons detected in PbPb collisions with the CMS

PRL 109 (2012) 222301

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PRL 109 (2012) 222301

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PRL 109 (2012) 222301

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Azimuthal Anisotropy of particle emission

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PRC 87 (2013) 042301

Good agreement with ALICE, except in

most peripheral events

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Azimuthal Anisotropy of particle emission

PRC 87 (2013) 042301

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Path length dependent Energy loss at high PT

Azimuthal Anisotropy of particle emission

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Di-hadron correlations: mountains, ridges, valleys

Hooker Valley, Mt Cook National Park, New Zealand

Pb+Pb

p+p p+Pb

JHEP (2011) 076

PLB (2013) 795 JHEP (2009) 091 D. Krofcheck IAS-CERN Workshop, Singapore 38

Summary

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sQGP Medium affects dijets and jets correlated with gamma/Z0

(gamma, Z and W particles appear to be unscathed)

sQGP Medium suppresses particle cross sections (seen in RAA) sQGP Medium “melts” early time probes (upsilon and J/psi) sQGP affects particle correlations (“ridges” seen in pp, pPb and PbPb?) Need reference pp data for meaningful PbPb comparisons CMS HI group looking at many observables to describe sQGP

In relativistic nucleus-nucleus collisions at the RHIC and the LHC

Backup slides

• We used dijets to compare PbPb collisions to pp

at different impact parameters and transverse

momenta

• Dijets can be strongly imbalanced in momentum as a result

of passing through the QCD medium

• We observe γ – jet correlations

Measuring the γ and jet energies may tell us about

the energy loss mechanism of in-medium partons.

Summary

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PLB 710 (2012) 256

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CMS preliminary

PRC 87 (2013) 042301

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Azimuthal Anisotropy of particle emission

Observed angular correlation between γ – jet in

PbPb collisions

γ – jet Correlation across PbPb overlap

PLB 718 (2013) 773

No significant angular decorrelation is observed for -jet pairs

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Observed angular correlation between the PbPb dijets

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Dijets in PbPb are more imbalanced than PYTHIA+HYDJET

Unbalanced Balanced

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